In one type of rotating magnetic recording rigid disk drives, each of the read/write transducers (or heads) is supported on a carrier (or slider) which rides on a cushion or bearing of air above the surface of its associated disk when the disk is rotating at its operating speed. The slider has an air-bearing surface (ABS), typically in the form of a plurality of rails, and is connected to a linear or rotary actuator by means of a relatively fragile suspension. There may be a stack of disks in the disk drive with the actuator supporting a number of sliders. The actuator moves the sliders radially so that each head may access the recording area of its associated disk surface.
The slider in this conventional disk drive is biased toward the disk surface by a small force from the suspension. The ABS of the slider is thus in contact with the disk surface from the time the disk drive is turned on until the disk reaches a speed sufficient to cause the slider to ride on the air bearing. The ABS of the slider is again in contact with the disk surface when the disk drive is turned off and the rotational speed of the disk falls below that necessary to create the air bearing. This type of disk drive is called a contact start/stop (CSS) disk drive. To provide wear resistance for the ABS in a CSS disk drive, a protective overcoat may be placed on the slider rails. U.S. Pat. No. 5,159,508, assigned to IBM, describes a slider with air-bearing rails having an amorphous carbon overcoat that is adhered to the rails by a silicon adhesion layer.
The magnetic recording disk in a CSS rigid disk drive is typically a thin film disk comprising a substrate, such as a disk blank made of glass or an aluminum-magnesium (AlMg) alloy with a nickel-phosphorous (NIP) surface coating, and a cobalt-based magnetic alloy film formed by sputter deposition over the substrate. A protective overcoat, such as a sputter-deposited amorphous carbon film, is formed over the magnetic layer to provide corrosion resistance and wear resistance from the ABS of the slider. A liquid fluorether lubricant is also maintained on the surface of the protective disk overcoat to prevent damage to the head and the disk during starting and stopping of the disk. Typically, the lubricant used on disks with carbon overcoats is made up of a first layer of lubricant which is bonded to the carbon and a second layer of free or mobile lubricant on top of the bonded lubricant.
Protective carbon overcoats for thin film disks and slider air-bearing surfaces are well known. They are typically formed by sputter deposition from a graphite target, and are generally called protective carbon overcoats, "diamondlike" carbon overcoats, amorphous carbon overcoats, or, in the case of those overcoats formed by sputter deposition in the presence of a hydrogen-containing gas, hydrogenated carbon overcoats. Tsai, et al. in "Structure and Properties of Sputtered Carbon Overcoats on Rigid Magnetic Media Disks," J. Vac. Science Technology A6(4), July/August 1988, pp. 2307-2314, describe such protective carbon overcoats and refer to them as amorphous "diamondlike" carbon films, the "diamondlike" referring to their hardness rather than their crystalline structure. U.S. Pat. No. 4,778,582, assigned to IBM, describes a protective hydrogenated disk carbon overcoat formed by sputtering a graphite target in the presence of Ar and hydrogen (H.sub.2). The carbon overcoats may also be formed by plasma-enhanced chemical vapor deposition (CVD) and may include nitrogen in addition to hydrogen, as described by Kaufman et al., Phys. Rev. B, Vol. 39, p. 13053 (June 1989).
In addition to the magnetic layer and the protective overcoat, the thin film disk may also include a sputter-deposited underlayer, such as a layer of chromium (Cr) or a chromium-vanadium (CrV) alloy, between the substrate and the magnetic layer and a sputter-deposited adhesion layer, such as a Cr, tungsten (W) or titanium (Ti) layer, between the magnetic layer and the protective overcoat.
To improve the wear resistance of the disk, as well as to maintain consistent magnetic properties, it is desirable to make the disk surface as smooth as possible. However, a very smooth disk surface in a CSS disk drive creates what is called "stiction". This means that after the slider ABS has been in stationary contact with the disk for a period of time, the slider tends to resist translational movement or "stick" to the disk surface. It is known that this "stiction" force can increase over time. Thus, the stiction force measured relatively soon after a CSS cycle is called "CSS stiction", while that measured several hours after a CSS cycle is called "rest stiction". Stiction is caused by a variety of factors, including static friction and adhesion forces between the disk and slider created by the lubricant or by capillary condensation of atmospheric water vapor. Stiction in a CSS disk drive can result in damage to the head or disk when the slider suddenly breaks free from the disk surface when disk rotation is initiated. Because the suspension between the actuator and the slider is relatively fragile in order to permit the slider to fly above the disk surface, sudden rotation of the disk can also damage the suspension.
To avoid the stiction problem associated with CSS disk drives, some disk drives are of the "load/unload" type. In this type of drive, the slider is mechanically unloaded from the disk, typically by means of a ramp that contacts the suspension when the actuator is retracted at power down, and then loaded back to the disk when power is turned on and the disk has reached a speed sufficient to generate the air bearing. Even in load/unload disk drives, however, stiction can be a problem in the event of failure of the load/unload system.
The more common solution to the stiction problem is to texture the disk. Typically, this is done by abrasive polishing of the disk substrate, which results in a texturing of the conforming layers deposited over the substrate. Thus, the carbon overcoat will reflect the texture placed on the substrate and reduce the stiction when the slider is resting on the disk carbon overcoat. However, texturing of the substrate adds to the disk manufacturing cost and complexity because it cannot be done in-situ in the conventional sputter deposition process chambers. U.S. Pat. No. 5,053,250, assigned to IBM, describes an in-situ process for forming a textured underlayer on the disk substrate. The '250 patent teaches the use of a metal material which, due to the heating of the disk substrate, is sputter deposited on the substrate as discontinuous liquid spheres. The subsequently deposited magnetic layer and carbon overcoat follow this discontinuous topology, resulting in a textured surface at the head-disk interface. Texturing of the entire disk substrate, whether by abrasive polishing or an in-situ process, has the additional disadvantage that the magnetic properties of the magnetic layer are degraded because the crystalline growth of the magnetic layer is adversely affected. This increases the data error rate in the disk drive. To avoid this problem, the texturing of the disk substrate may be limited to a nondata band, called the landing zone, where the slider is moved when the disk drive is stopped. The landing zone, which adds to the complexity of the drive electronics, is required to prevent the substrate texturing from adversely affecting the magnetic properties of the disk in the data region.
As an alternative to texturing the substrate, texturing of the disk protective overcoat has been suggested. This can be accomplished by mechanical processes, such as abrasive polishing, or by chemical or laser etching, as described in IBM Technical Disclosure Bulletin, October 1989, p. 264. Another type of overcoat "texturing", as described in U.S. Pat. No. 5,030,494, assigned to IBM, involves cosputtering the carbon with other material additives, such as tungsten carbide, to form clusters of the additives that project above the relatively smooth carbon overcoat surface and present a discontinuous head-disk interface. These types of prior disk overcoat texturing techniques either involve additional complex and costly ex-situ process steps or result in an overcoat which is not the preferred continuous film of amorphous carbon.
What is needed is a thin film magnetic recording disk with a continuous textured protective overcoat formed by a conventional in-situ process. The disk overcoat must reduce stiction, be wear resistant, and not affect the magnetic recording performance of the disk drive.